Epitaxial Synthesis of Oxide Dirac Semimetal CaNbO₃ Thin Films

Dirac/Weyl semimetals exhibit massless behaviors, leading to high carrier mobility and exotic quantum transport phenomena. Until now, only a limited number of studies have been conducted to explore Dirac/Weyl semimetals in oxide system, because the observation of a topological band structure to enable quantum transport is rare in oxide materials. Here, we report epitaxial synthesis of high-quality CaNbO₃ thin films by pulsed laser deposition on various substrates and their structural and physical properties. While bulk CaNbO₃ is orthorhombic, thin films revealed a delicate change of the structure depending on the growth conditions, including the type of substrates, thickness, and strain. Both tetragonal and orthorhombic phases with different octahedral symmetries were observed through X-ray Bragg rod measurements. Epitaxial strain is found to effectively manipulate oxygen octahedral symmetry from a⁰a⁰c^- to a^-b⁺c^- / a⁺b^-c^- along with structural phase transition from tetragonal phase to orthorhombic phase. Furthermore, high-mobility transport was achieved on CaNbO₃ films along with a large linear magnetoresistance (LMR), which is one of the representative signatures of a Dirac semimetal.